The present invention relates to a polyolefin composition having high rigidity and high impact resistance. More particularly, the present invention is concerned with a polyolefin composition comprising a propylene polymer, a specific ethylene/.alpha.-olefin copolymer and mica and having high rigidity and high impact resistance.
In recent years there has been a marked trend to the reduction of weight from the standpoint of resources saving and energy saving particularly in the fields of automobile industry and electric industry. For example, in the automobile industry, there is now a strong tendency to form various components, including outside plating, bumper and instrument panel, from resins. Similar tendency is occuring also in the field of household electrical appliances and of electric wire coating. Substitution for conventional materials such as steel plate and aluminum, as well as reduction in thickness of conventional resins, have been being tried actively.
From such point of view, various resins having high rigidity and high impact resistance have already been put to practical use. For example, in the field of polyolefin resins there have been developed, in an effort to attain high rigidity and high impact resistance, such compositions as blend compositions comprising various inorganic fillers and propylene block copolymer superior in impact resistance (see Japanese Patent Publication Nos. 43057/1984 and 3417/1985), compositions obtained by adding a nucleating agent to the above blend compositions (see Japanese Patent Publication No. 1741/1984), and blend compositions comprising inorganic fillers, polypropylene and ethylene-propylene rubber (see Japanese Patent Laid Open No. 136736/1976, Japanese Patent Publication No. 16982/1985 and U.S. Pat. No. 4,229,504). Usually employed as inorganic fillers are calcium carbonate, talc and glass fiber. The use of mica is also known (see Japanese Patent Laid Open No. 108241/1983).
However, it is desirable that both rigidity and impact resistance be as high as possible. And when polypropylene resins are blended with inorganic fillers for the enhancement of strength and rigidity, the resulting blends tend to be markedly reduced in impact resistance. Further, impact resistance at low temperature is also very important in practical use. When these points are taken into consideration, such known compositions of high rigidity and high impact resistance as inorganic filler/propylene block copolymer blend composition and inorganic filler/polypropylene/ethylene-propylene rubber blend composition are still insufficient in point of performance and the development of compositions further superior in rigidity and impact resistance is desired.